This invention relates to pulsed power linear actuators and methods for controlling the stroke force of linear actuators, and more particularly to using kinetic energy and electromagnetism in controlling the stroke force and position of linear actuators.
The use of linear actuators is well known throughout various industries. For example, many manufacturing operations utilize linear actuators to control, with a high degree of precision, the movement of linear moving members. Prior mechanical linear actuators have relied on physical linkage between the drive mechanism and the stroke arm, thereby engendering friction and wear and so requiring lubricants. Even with lubricants, such actuators must often be replaced or reconditioned.
To avoid the problems caused by friction, actuators have been developed which use magnetic fields to support and separate components. These electromagnetic actuators essentially have no physical contact between their stationary and moving components. Without physical contact, no lubrication is necessary and little wear occurs, resulting in nearly unlimited life for the actuators under normal operating conditions.
Unfortunately, conventional electromagnetic actuators also have limitations which cause them to be complex, costly, and have restricted performance. For example, in conventional electromagnetic actuators, the output force of the actuator is typically determined as a function of an electrical input signal. This input signal may include a stored charge (i.e., capacitors) for producing a current pulse which creates induced currents in a driver component and forces the driver from its stationary position. One such apparatus is described in Zieve, U.S. Pat. No. 4,990,805. Zieve shows a bank of large, bulky capacitors which are required to create the forces necessary to properly operate the actuator. These capacitors severely limit the possible applications for such a device.
A conventional electromagnetic actuator which does not require a capacitively stored charge is described in Stuart et al. U.S. Pat. No. 5,099,158. Stuart describes a linear actuator having a coil made of at least two segments that are exposed to a magnetic flux source which generates flux in radially opposing directions. A command signal is applied to the center of the coil to cause current to pass through the segments in opposing directions producing an additive force (i.e., the sum of the force due to the inward radial flux and the force due to the outward radial flux). Even though this actuator generates a relatively large force from a relatively small input signal, the output force is still limited by the amplitude of the input signal. In addition, the input signal is applied to the coil by either brushes (which will wear out), or by physically connecting the coil to the moveable assembly (which severely restricts the stroke length and force with which the moveable assembly may move).
In recent years, there has been an increasing demand for linear actuators which have a high force per unit mass rating. This has been due to the desire to replace bulky, heavy, high-maintenance hydraulic systems with lighter, more reliable components in such applications as jet aircraft control surfaces and landing gear, and robotics. Conventional electromagnetic actuators simply cannot generate the force per unit mass required due to the fact that they draw all of their energy and power from a single electrical input.
In view of the foregoing, it is an object of this invention to provide improved linear actuators which derive energy and power from multiple sources to provide increased force per unit mass.
It is also an object of this invention to provide methods for driving linear actuators from multiple sources to provide increased force per unit mass.
It is another object of this invention to provide electromagnetic linear actuators which are uncomplicated, effective, reliable and inexpensive.